1. Field of the Invention
This invention relates generally to steering column assemblies and particularly to an intermediate shaft for a steering column which offers reduced backlash and vibration and improved lateral stability than prior designs.
2. Discussion of the Related Art
Steering wheels of automobile and other vehicles are, in most cases, connected by one or more serially arranged shafts from the steering gear box to the steering wheel of the vehicle. In the early designs, a single solid shaft was connected at one end to the steering gear and at the other end to the steering wheel. Later designs incorporated one or more universal joints for routing the shaft from the steering wheel to the steering gear. It was found that solid steering column shafts presented a significant danger to drivers.
In later designs it was common to connect the steering wheel to the steering gear by a pair of tubular, concentrically positioned members which could telescope relative to one another, but were fixed rotationally. The tubular members had interconnecting end portions to permit rotation or transfer of torque from the steering wheel to the steering gear. However, these designs present substantially the same danger as prior designs because the telescoping distance was short in comparison to the shaft assembly. Moreover, as in the previous designs, the shaft transmitted vibrations produced by the road and engine to the steering wheel, producing numbness and fatigue in the operator's hands. Additionally, the interconnection of the tubular members created substantial backlash or nonresponsiveness in the steering wheel due to the gap between the concentrically arranged tubes.
U.S. Pat. No. 5,243,874 illustrates a more recent structure for use in steering columns. A pair of telescoping members are provided having a preselected cross-sectional configuration that facilitates the insertion of one tubular member in the other. The surface configuration of the interconnecting portions is complementary to prevent rotation of one with respect to the other. The outer surface of the internal member is spaced from the inner surface of the outer member forming an annulus which receives a thermosetting resinous material injected therein at an elevated temperature. The thermosetting resin shrinks upon cooling to form a sleeve having a cross-sectional area less than the annulus to permit telescopic movement of the inner tube. The disadvantage of the construction is the substantial backlash which exists as a result of the shrinkage of the resin. Another problem is the need to maintain the concentric orientation of the inner tube with respect to the outer tube during the injection step so the inner tube does not become eccentric with the rotational axis.